Control of intervertebral disc degeneration via matrix-mediated delivery of platelet-derived growth factors

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Summary There is no successful biologic treatment for intervertebral disc degeneration (IDD). The goal of this proposal is to utilize a hydrogel-based engineering approach to deliver PDGF to intervertebral disc (IVD) tissue and establish PDGF as a potent inhibitor of IDD. We also aim to define the mechanisms underlying its effects on normal and diseased nucleus pulposus (NP) and annulus fibrosus (AF) cells using human IVDs as well as preclinical models of IDD. The scientific premise for the proposed work is a rigorous body of published evidence demonstrating that PDGF- BB, as well as PDGF-AB can stimulate disc cell growth and/or inhibit their programmed cell death in vitro. Our compelling preliminary data in vivo point to an anti-apoptotic effect of PDGF-BB in a rabbit puncture model, which led to restored disc height and enhanced mechanical properties of the treated discs compared to untreated controls. It is based on these encouraging data and other molecular preliminary data demonstrating that these anti-apoptotic effects may be mediated through the transcription factor Runx1, that we postulate the novel hypothesis that sustained exposure of the NP and AF to PDGF will repress IDD progression through controlling Runx1 activity. To test this hypothesis, we will first compare the effects of PDGF-BB and PDGF-AB on normal versus diseased human AF and NP cells cultured in high density. We will then determine the molecular mechanisms underlying the anti-degenerative effects of PDGF on disc cells through transcriptomic and functional analyses involving RUNX1 and other signaling molecules (Aim 1A). The validation of Runx1 function in PDGF-mediated effects will also be examined in vivo using a new gain of function mouse model (Aim 1B). In the second Aim, we will fabricate and validate the functionality of an injectable biomaterial capable of sustaining the exposure of disc cells to PDGF-BB (Aim 2A). We will then establish therapeutic modalities for long-term inhibition of IDD in vivo by PDGF-BB using a rabbit disc puncture model (Aim 2B). Our proposed work will provide seminal information about the mechanisms underlying PDGF’s effects on the IVD and the role of Runx1 in IDD. The mechanistic data will help identify new therapeutic targets to treat IDD.